Process for electrodeposition of cadmium



Patented May 31, 1960 PROCESS FOR ELECTRODEPOSITION F CADMIUM Simon W. Strans, 3801 Connecticut Ave. NW., Washington 8, D.C.; and Peppino N. Vlannes, 8535 Van Buren Drive, Fort Washington Forest, Washington 22, D.C.

No Drawing. Filed Dec. 19, 1958, Ser. No. 781,810

3 Claims. (Cl. 20414) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a process for the electrodeposition of cadmium.

Electroplating with cadmium is customarily done from aqueous cyanide bath. While this process has a num-' ber of good qualities, it is a well-known source of introduction of hydrogen into metals. Hydrogen is introduced into the metal by reason of the fact that both hydrogen and cadmium are deposited at the surface of the cathode and part of the deposited hydrogen is absorbed by the metal being plated. The presence of hydrogen in the metal reduces the fatigue strength of the metal through hydrogen embrittlement.

In recent years there has been an increasing incidence of service failures in which high strength steel articles which have been madmium plated by the cyanide bath process have failed by delayed fracture. This phenomenon of delayed fracture, also referred to as static fatigue, is known to be associated with the presence of hydrogen in the steel. Delayed fracture is fracture of the metal after a period of time under an essentially constant stress much lower than the yield strength of the metal.

It is a principal object of the present invention to provide a new process for the electrodeposition of cadmium. It is also an object to provide a process for electroplating with cadmium in which deposition of hydrogen and consequent hydrogen embrittlement of the metal to be plated is markedly reduced over that occurring in the aqueous cyanide bath process.

The above and other objects of the invention can be accomplished by the process of our invention which comprises electrodepositing cadmium from a liquid bath which comprises a solution of cadmium acetate and methanol at a temperature within the range of from about --70 C. up to about C. At temperatures above about C. plating does not take place. A preferred range of operating temperatures for the process of our invention is from about 10 C. to 10 C.

Electroplating baths suitable for use in the process of our invention are made up by simply dissolving cadmium acetate in methanol to concentrations sufficient to give platings on the metals. The methanol used may be of high purity or of commercial or technical grade and anhydrous or practically so or contain small amounts of water generally up to about 5% by volume. The cadmium acetate may be anhydrous or a hydrate. Thus the baths may be anhydrous when made up with dry methanol and anhydrous cadmium acetate, or they may contain water when either non-dry methanol or a hydrate of cadmium acetate or both are used. In small amounts,

- for example, up to about 5% by weight, the water content of the baths is not an important or controlling factor in the process.

The composition of typical electroplating baths for use in the process of our invention appear in the table below, of which those of about 40% cadmium acetate saturation are preferred.

Cadmium Approximate Methanol, ml. AcetateBHzO, Saturation,

grams percent The electroplating process of our invention, aside from the composition of the bath and the necessary low temperatures, can be carried out in conventional manner. The vessel for the plating bath may be of any suitable design. The plating may be performed from a static cell or a rotating barrel with good results in reduction of hydrogen deposition and hydrogen embrittlement of the metal to be plated. The vessel is preferably made of a non-conducting material such as a plastic, for example, polyvinyl chloride, polyethylene, rubber, glass or earthenware. For operation of the process at the low temperatures, the plating vessel is supported in a cooling bath in'conventional or other manner using a liquid coolant such as cold circulating brine, or solid carbon dioxide. The anodes are cadmium and may be in the form of balls, strips, liners, rods, etc., connected to a source of current and placed in contact with or suspended in the bath. The current supplied to the cathode may be such as to give a current density for plating of from about 7 to 30 amperes per square foot of cathode area. The cathode should be clean and smooth following known good plating practice. For steel, in particular ultra high strength steel, 2. pickling or acid cleaning step should be omitted to preclude hydrogen embrittlement of the steel known to be caused by the acid immersion procedure.

Electrodeposition of cadmium by the process of our invention can be made on mild and high-strength steels and on iron, copper and copper-rich alloys, such as brass, and on other metals which are plated with cadmium. The process is best conducted at temperatures in the region of zero centigrade, for which a suitable operating range is from about -10 C. to 10 C., as has been set forth above.

Comparative tests performed with the use of a cylindrical notched bar of A181 4340 steel of approximately 285,000 p.s.i. ultimate tensile strength as substrate and plating of the bars with cadmium from baths of the composition set forth in the table above and from a standard aqueous cyanide bath demonstrated the marked reduction in hydrogen deposition and hydrogen embrittlement to be obtained by electroplating with the process of our invention. The current density was 15 amperes per square foot in each case for the platings by the process of the invention and 25 amperes per square foot for the plating by the cyanide bath process. The platings by the process of the invention were performed at zero centigrade. The plating from the aqueous cyanide bath was, in accordance with general practice, performed at room temperature. The plating time in all cases was for 15 minutes. The plate thickness on the barrel of the specimens was about .0005 inch average. The steel bars were cleaned for plating by sandblasting rather than by pickling in order to eliminate the hydrogen embrittlement known to be caused by pickling alone.

The plated steel specimens were evaluated for hydrogen embrittlement by delayed fracture test. The test was that of Raring and Rinebolt, ASTM Bulletin No. 213, pages 74-76, April 1956. The load applied was 3 75% of the ultimate tensile strength of the unplated bar. This represents very severe test conditions. Whereas the specimen plated with cadmium by the cyanide bath process fractured on loading, the specimens plated with cadmium by the process 'of the invention d'idhot fracture within the 100 hour test-periodI j Another comparative test was made by the older tensile testing method which involves application-of an increa'sing load in tension on the specimens. The steel-specimens were in all respects the same as those used in the delayed fracture test except that they were in the form of rotating-type cantilever tensile bars. In this test, .the

specimen undergoes reduction in area with increasing load until break or fractureoccurs. Therextent of reduction in area of the specimen before fracture is the measure of the tensile strength of 'the 'm'e'tal undertest.

The specimen steel bars plated with cadmium by the cyanide bathprocess underwent a reductioninarea of only 8% before fracture as against a reduction in area of about 45% for the specimen steel bars which flrad been plated with cadmium by the process of the invention and like bars of the steel which were unplated.

Since the principle of the invention herein described may be variously practiced without departing from the spirit or scope of the invention, itis to be understood that specific embodiments of the invention appearing in the above description are to be taken as illustrative and not in limitation except as may be required by the appended claims.

What is claimed is:

1. In the electrodeposition of cadmium, the improvement which comprises electrodepositing cadmium from a liquid bath comprising a solution of cadmium acetate and methanol at a temperature in the range of from about -70 C. to about 20 C."

2. In the electrodeposition of cadmium, the improvement which comprises nelectrodepositin'g cadmium from a liquid bath comprising a solution of cadmium acetate and methanol at a tempera e in the range of from about 10 C. to about 10 C.

' 3. In the .electrodepositio'n of cadmium, :the improvement which comp is s electroplating cadmium from a liquid bath comprising a solution er cadmium acetate and methanol of about 40% cadmium acetate saturation at a temperature in the range of from about .1() C. to about 10 C.

References Cited in the file of this patent V UNITED STATES PATENTS OTHER REFERENCES Chemical Age, March 30. 1946, page 336. 

1. IN THE ELECTRODEPOSITION OF CADMIUM, THE IMPROVEMENT WHICH COMPRISES ELECTRODEPOSITING CADMIUM FROM A LIQUID BATH COMPRISING A SOLUTION OF CADMIUM ACETATE AND METHANOL AT A TEMPERATURE IN THE RANGE OF FROM ABOUT -70*C. TO ABOUT 20*C. 